P (Watt), namely:

P=VI=I²R = V² /R

where equation (1) has been used to express P in terms of 1² and in terms of V².

The power absorbed by the resistor appears in the form of heat. The physical size of the resistor

determines the amount of power that it can safely dissipate. This amount is referred to as the power

rating. The dissipation of power that exceeds the power rating can damage the resistor physically.

When the resistor gets heated due to excessive power dissipation, its resistance changes. It will

either increase or decrease depending on the temperature coefficient. A carbon resistance is

expected to increase as the temperature increases.

Resistances that are operated above the power rating will deviate from the straight-line relationship

between V and I. The resistor in this case is operating in the non-linear region. In such a case, the

resistance is no longer equal to the slope of the V versus I graph. It may however, be calculated

using the ratio V/I.

Procedure:

You will be supplied with sets of 3 resistors.

1. Find the nominal value and the tolerance of each resistance using the Resistor colour code

chart shown below. Note the relation between the power rating and the physical size of the

resistance.

2. Using the digital multi-meter as an ohmmeter, measure and record the resistance of each

resistor.

3. Connect the circuit as shown in Figure. 2 for R = 100 2 and perform the following:

a- Set the source voltage V3 to 10 V.

b-Measure V and I.

d- Record your results in Table 1./n+ A

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Fig. 2a : Series Connection

I

Fig. 2b: Parallel

Connection

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